Fossil Shells.

Mollusks (Phylum Mollusca), especially bivalves (Class Bivalvia, clam-like creatures) and gastropods (Class Gastropoda, snail-like creatures) lived in the ancient seas that are now Las Vegas. Bivalves can occasionally be found in Paleozoic and Cenozoic sedimentary rocks, but gastropods are less frequently seen.

A nice place to see Paleozoic bivalves is Blue Diamond Hill (Fossil Canyon Trail and Rock Garden Trail) at Red Rock Canyon NCA, and a nice place to see Cenozoic bivalves is along Cottonwood Wash in Lake Mead National Recreation Area. For gastropods, there is a nice outcrop in the Desert National Wildlife Range about 5 miles out the Mormon Well Road.

Being protected areas, however, these are places to look and marvel, but leave the rock hammer at home and don't collect specimens.